Process for pyrolyzing hydrocarbons



2,985,698 PROCESS FOR PYROLYZING HYDROC R ONS Nikolaus Pechtold and Rudolf Wirtz, Frankfurt am Main, Germany, assignors to Farbwerke Hoechst Aktlengesellschaft vormals Meister Lucius & Brunlng, Frankfurt am Main, Germany, a corporation of Germany Filed Sept. 26, 1958, Ser. No. 763,525 Claims priority, application Germany Sept. 27, 1957 14 Claims. (Cl. 260-683) The present invention relates to a two-stage pyrolysis of hydrocarbons.

It is known that hydrocarbons containing two or more carbon atoms (hereinafter defined as paraffinic hydrocarbons) can be cracked by introducing these hydrocarbons, if desired after they have been separately preheated, in liquid or vapor form, into a current of hot combustion gases and chilling them after a short period of reaction. The cracked products so obtained consist substantially of acetylene, ethylene and higher olefins. The combustion gases are produced by burning hydrogen and/or any desired carbonaceous compound with oxygen in a combustion chamber and cooling the hot gases to the optimum temperature by addition of a secondary gas, for example steam and/or hydrogen.

It is also known that methane can be cracked in a manner similar to that described above, but in this case the pyrolysis must be carried out at a temperature higher than that used for cracking paraflinic hydrocarbons, which is quite plausible considering the different free energy values. The temperature down to which a reaction occurs (reaction end temperature) varies in the case of parafiinic hydrocarbons between 700 C. and 1250 C.; this temperature must be the higher the greater the desired yield of acetylene. In the pyrolysis of methane such temperature must amount to at least 1400-1600 .C., if a considerable portion of methane'shall be cracked. The amount of heat dissipated by the chilling which is lost for the chemical reaction when cracking methane, is accordingly much greater than it is in the pyrolysis of paraffinic hydrocarbons. Since such amount of dissipated heat can only be used for producing steam, if at all, it is evident that such high temperatures interfere with the economy of the methane pyrolysis.

The present invention provides a process for pyrolyzing hydrocarbons, wherein methane is introduced 'into' a hot combustion gas free from molecular oxygen in excess to produce a hot gas vmixture, and wherein at least one parafiinic hydrocarbon containing at least two carbon atoms is introduced separately, in finely divided form, into said hot gas mixture, and the reaction mixture is chilled.

The term parafiiniehydrocarbon as used herein is intended to mean non-aromatic hydrocarbons or mixtures of hydrocarbons containing more than 2 carbon atoms, which consist substantially of saturated, straight chain, branched or cyclic hydrocarbons or mixtures thereof. The term "paratlinic hydrocarbons" is also intended to mean saturated hydrocarbons containing small amounts of aromaticor olefinic hydrocarbons. Still further, it is intended to comprise saturated hydrocarbons contaminated by small amounts of sulfurous and/or nitrogenous compounds as they are obtained in chemical processes or, more especially, as they appear in natural hydrocarbons.

Suitable parafiinic hydrocarbonsare gaseous, liquid and solid, non-aromatic hydrocarbons; solid hydrocarbons may be first melted or dissolved in liquid hydrocarbons and then used in the liquid state. More especially, it is advantageous to use gaseous or liquid hydrocarbons as obtained in processing petroleum or in the hydrogena- H United States Patent tion of carbon monoxide (Fischer-Tropsch-process). It is especially advantageous to employ saturated hydrocarbons carrying up to 30 or more carbon atoms, such as ethane, propane, butane, pentane, heptane, octane, decane, or dodecane. There may also be used branched hydro: carbons, for example isobutane, isohexane, isoheptane or isooctane. Still further there may be used saturated cyclic hydrocarbons, such as cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclodecane or bicyclododecane. These hydrocarbons are advantageously used in the form of commercial mixtures, such as petroleum distillates or hydrocarbon oils, for example topped Kuweit oil, or in the form of industrial or natural gases. There may also be employed parafiinic hydrocarbons containing small amounts of olefins. such as ethylene, propylene, normal or isobutylene. The hydrocarbons are used in either the gaseous or liquid state; in the latter case they are introduced into the combustion chamber in fine distribution, for example by atomization. The term "fine distribution" as used for the purposes of this invention is not only intended to include fine atomization of liquid hydrocarbons, but it is also intended to include the use of hydrocarbons'in gas and vapor form.

The combined pyrolysis olfers the advantage of being more economic in view of the fact that the energy is utilized to a degree which could only be reached so far by using parai'linic hydrocarbons; notwithstanding that it is possible to partially replace these hydrocarbons by the cheaper methane which may be used, for example in the form of earth gas. In other words, the very same amount of heat hitherto necessary to crack a certain amount of methane, enables at the same time an additional quantity of parafiinic hydrocarbons to be pyrolyzed.

Accordingly, a considerably reduced amount of heat is required for producing the same amount of a desired pyrolyzed product, more especially olefins and acetylene. The process of this invention will therefore be used when it is desired to better utilize the energy expended in the methane pyrolysis by subsequently cracking parafllnie hydrocarbons, or when it is intended to reduce the costs of the starting material in pyrolyzing paraffinic hydrocarbons by combination with a methane pyrolysis (at the same degree of energyutilization) In the latter case the expenditure for the secondarygas and the additional hydrogen may be saved, since methane may be substituted for both gases, either wholly or partially. The invention offers the further advantage that the reaction product obtained contains much more unsaturated compounds than that obtained in the pyrolysis of methane.

With a view to the experiences so far gained in the art, it could not be expected that such combined cracking process would be possible; the combined cracking process can only be carried out successfully if the reaction time for the second cracking, which takes place at a temperature lower than that in the first cracking, is still short enough to prevent a noticeable decomposition of the acetylene produced in the first stage of cracking. For this reason the temperaturemust not have fallen to too low a degree following the first stage, since periods of stay would otherwise be necessary during which a noteworthy portion of the acetylene formed in the first cracking stage would decompose. On the other hand, it is necessary to add the second hydrocarbon only when the Pa tented May 23, a '1, 961

spasms duce the hot combustion gas; a possible addition of steam or hydrogen should not exceed calculated upon the amount of the combustion gas. The combustible and the gases containing oxygen used may have been preheated to a temperature of between about 200 C. and abou=t800 C., preferably between about 400 C. and about 600 C. The combustion gasso produced is free from molecular oxygen in excess and enables temperatures of more than 2000' C., and more especially of up to 2400" C. to about 2600' C., to be reached.

As combustible there may advantageously be used gaseous or liquid or fusible solid hydrocarbons in liquefied form, in the latter case in a finely divided state. may also be used hydrogen, carbon monoxide or water gas containing an excess of hydrogen and/ or carbon monoxide and, more especially, gases which consist substantially of methane, such as natural gases. It'is especially advantageous to use pure hydrogen or a mixture of pure hydrogen with one of the aforesaid combustibles. From an economical point of view it is especially useful to use as combustible the residual gas obtained from the crack gas after separation of unsaturated compounds and carbon dioxide; this residual gas consists substantially of hydrogen, carbon monoxide and methane.

The methane which, advantageously, has been preheated to a temperature of about 400 C. to about 800 C., is introduced into the combustion chamber at a place near the outlet of said chamber. The combustion chamher is connected with a reactor which is so dimensioned that the time of stay of the gas mixture in said reactor is within the range of about 10- to about 10- seconds, and in which the methane is cracked to substantially produce acetylene and carbon monoxide. The amount of methane introduced is so regulated that the reaction end temperature is above 1200' C. and, advantageously, between 1400 C. and 1600 C. The paraffinic and advan- There tageously also preheated hydrocarbons which participate in the second stage of the cracking reaction are added in a second reactor by means of one or more nozzles. These hydrocarbons may have been preheated, for example to 50 C. up to almost 500 C., preferably to 200 C. to 400 C. In the second reactor which is designed similar to that used in the first reaction stage, the hydrocarbons are cracked within a time in the range of 10- to 10'- seconds and furnish substantially ethylene. The hot gases are fairly rapidly chilled at an end temperature which is between 700 C. and 1100 C. depending on the amount of parafiinic hydrocarbons used, washed, and the gases obtained are separated from one another in the usual manner.

The process described above may also be influenced by varying the pressure conditions. in this case, the combustion is brought about in the combustion chamber (combustion zone) under a raised pressure of about 2 to about 21 atmospheres absolute, preferably 3 to about 9 atmospheres absolute. The second reaction chamber 3 (second zone of reaction) is advantageously kept under a certain diminished pressure of about 0.1 to 0.9 atmosphere absolute, preferably 0.5 to 0.9 atmosphere absolute. As a consequence of this measure, a pressure is produced in the first reaction chamber which is situated between the combustion chamber 1 and the second reaction chamber 3; the design of the first reaction chamber, for example the constricted opening arranged between 1 and 2 and/or 2 and 3 enables this pressure to be adjusted to about 0.9 atmosphere absolute to about 2 atmospheres absolute, preferably about 1 atmosphere absolute to about 1.4 atmospheres absolute. Such regulation of the pressure conditions as described above leads to an increased yield of unsaturated hydrocarbons.

Apparatuses suitable for use in carrying out the proces of this invention are illustrated diagrammatically in Figures 1 and 2 of the accompanying drawing.

To efiect the combustion at the desired high temperature, there may be used, for example, a metal burner 1 into the head of which the combustion gases and oxygen or the gases rich in oxygen are introduced tangentially or radially. Towards the end of the combustion zone, a

small amountof steam, hydrogen or a mixture of these- 3 two gases, may be admixed as a secondary gas. In the neck of the burner, methane is introduced through one or advantageously several preferably radial nozzles, the number of nozzles used being so selected that the methane is rapidly mixed with the combustion gases so as to avoid that the uncooled combustion gases come into contact with the wall of the reactor.

Reactors 2 and 3 consist, for example, of cylindrically or conically shaped metal tubes, betweeen which a constricted zone may be arranged similar to that fdrming the transition zone between the combustion chamber and reactor 2. The dimensions of this constricted zone enable the pressure conditions which prevail in the reactors to be regulated. In view of the high temperature, the reactors may be provided at the inside with a ceramic lining, or may be cooled from the outside as shown in Figures 1 and 2 of the accompanying drawing. In special cases both reactors may form a uniform tube with appropriately arranged nozzles for the supply of aliphatic hydrocarbons. The supply pipes may be provided with a separate cooling jacket to avoid superheating, or the cooling jacket of the reactor may undertake the cooling as shown in Figure Z. The combustion chamber may likewise be lined at the inside with ceramic material or may be cooled from the outside, for example with water, in order to protect the combination chamber against the influence of the high temperatures used.

The combined pyrolysis described above can also be used in the partial methane combustion process. In this case, the reactants are preheated to a temperature in the range of between about 400 C. and about 800' C. and methane is burned with a deficiency of oxygen in a burner of known design. Thecombustion and methane cracking take place in one stage; paraflinic hydrocarbons are then added separately in the manner described above.

cracked and chilled.

The following examples serve to illustrate the invention, but they are not intended to limit it thereto:

Example 1 28.2 Nmfi/h. (normal cubic meters; NIP.) of hydrogen were burned with 12.9 NmF/h. of oxygen under a pressure of- 25 atmospheres absolute in a water-cooled burner It. In the neck (A) of the burner, the. hot combustion gases (about 2.400 C.) were admixed with 8.6 NmF/h. of methane which had been preheated to 400' C.; the methane was introduced through 2 radial nozzles;

the mixture so obtained was then pyrolyzed within a time of stay of 0.5.10- seconds in a cylindrically shaped reactor 2 lined with ceramic material.' In the constricted zone (B) 5.0 kg./h. of light benzine (slop benzine; boiling range: 30-105 C.) were added through two water-cooled nozzles; the benzine had previously been evaporated and heated to 250' C. The benzine was cracked in a reactor 3 within 3.10 seconds and chilled with water. 30.4 Nmfi/h. of gas was obtained (composition A). When following the methane pyrolysis, the cracked gases were chilled without addition of benzine, 24.6 NmJ/h. of gas was obtained (composition 13).

Exmrple .2

he experiment was carried out in; an apparatus described in the preceding example that no constricted zone was provldedbetween the two reactors. 27.2 NmA/h. of hydroien were burned with 13.6 Nmfi/h. of oxygen and the combustion gas produced was admixed with 15.0 Nm./h. of methane which had been preheated to 600 0.; in the second stage there were then added 3.8 kg./h. of a petroleum fraction (boiling range: 60-180 C.) which had previously been evaporated and preheated to 300' C. 41.5 Nm'lh. of cracked gas (composition A) were obtained as compared with 37.8 NmJ/h. of cracked gas (composition B) with direct chilling following the methane pyrolysis without addition of petroleum fraction. V

Exanplc 3 20.5 NmP/h. of recycled gas containing 56.2% of H 11.4% of CH 29.4% of CO, 3% of N, were burned with 13.9 Nm. /h. of oxygen under a pressure of 5.5 atmospheres absolute in awater-cooled burner 1 provided with a nozzle (A) narrower than that used in Example 1. 2.0 kg./h. of steam were additionally introduced into the burner as secondary gas. In the neck of theburner, the hot combustion gases (about 2500 C.) were admixed with 11.6 NmF/h. of methane which was introduced through four radial nozzles and had been preheated to 600 C.; the gases were then cracked under a pressure of 1.2 atmospheres absolute; a temperature of about 1400 C. was reached. In the second stage 6.2 kg./h. of light benzine ("slop benzine; boiling range: 30-105' C.) which had been evaporated and preheated to 250 C., were added and cracking was carried out under 0.7 atmosphere absolute; the cracked gases were then chilled with water; a temperature of about 1000' C. was reached. The reactors used were the same as those described in Example 1. 39.9 NrnP/h. cracked gas (composition A) were obtained as compared with 34.2 NmP/h. of cracked gas (composition B) with direct chilling followingthe methane pyrolysis without addition of benzm' e.

Corn ltlon Com sltlon A, ercent B, ereent by volume by volume 40. 8 46. 2 ll. 12. 8 2o. 8 M 3 ll. 0 8. 2 0. 0 6. 7 0. l 0. 4 0. 0 0 2. 8 2. 4

Example 4 29.4 Nm.=/h. of methane and 18.1 NmQ/h. of oxygen were preheated to 600 C., mixed and burned in a combustion chamber lined with ceramic material. In view of the oxygen deficiency a greater amount of acetylene was obtained in addition to the combustion gas. 10.2 kgJh. of light .benzine, which had previously been evaporatedand heated to 300 C., were then injected into the hot combustion gas. When the cracking reaction was complete, the. gases were chilled with water. 63.8 Nm.'/h. of gas were obtained (compodtion A) while only 55.3

withtheexception 6 Nari/h. otgas (composition B) were obtained when the gases were chilled following the partial methane cornbustion without addition of benzine.

Composition A, Percent B, by volume by volume We claim:

1. In the'process for the manufacture of unsaturated C, hydrocarbons by introducing methane into a combustion gas which is free from an excess of molecular oxygen, the improvement which consists in adding to the hot gaseous mixture thus obtained and having a temperature in the range from about 1600' C. to about 1200' C., at least one paraflinic hydrocarbon containing at least two carbon atoms, in an atomized form, and adjusting the temperature of the hot gaseous mixture after the pyrolysis of the said parafl'inic hydrocarbon'to a range from about 1100' C. to about 700 C. by regulating the amount of said paraflinic hydrocarbon, and chilling. the reacted mixture.

2. A process as claimed in claim 1 wherein up to 10% of a secondary gas is added to the hot combustion gas prior to the introduction of the methane, said secondary gas being selected from the group consisting of hydro- 45 about 400 c. to about 800' c.

6. A process according to claim 1, wherein the said paratfinic hydrocarbon is preheated to a temperature in the range from about 200 C. to about 400 C.

7. A process according to claim 1, wherein the fuel and the oxygen used for the burning of the fuel are preheated to a temperature in the range from about 200' C. to about 800 C.

8. A process according to claim 1, wherein in the combustion zone a pressure from about 3 to about 9 atmospheres (absolute) is maintained.

9. A process according to claim 1, wherein in the second reaction zone (3) a pressure from about 0.5 to about 0.9 atmospheres (absolute) is maintained.

10. A process according to claim 1, wherein in the first reaction zone (2) a pressure from about 1 atmosphere (absolute) to about 1.4 atmospheres (absolute) is maintained.

11. In the process for the manufacture of unsaturated C, hydrocarbons by introducing methane into a combustion gas which is free from an excess of molecular oxygen, the improvement which'consists in adding to the hot gaseous mixture thus obtained and having, after a reaction time of 10- to 10" seconds, a temperature in 7 by regulating the amount 01 said paramnic hydrocarbon, and chilling the reacted mixture.-

12. A process for preparing unsaturated C hydrocarbons which comprises burning a combustible material of the group consisting of hydrogen, a carbon monoxide, methane and mixtures thereof with oxygen in a combustion zone to form a stream of combustion gas free from excess molecular oxygen and having a temperature between about'2000 and 2600 C., introducing methane into said stream of combustion gas in a first pyrolysis zone at a rate sufiicient ,to convert said methane into acetylene and carbon monoxide and reduce the temperature of the stream of combustion gas to between about 1200 and 1600 C., introducing, in a second pyrolysis zone, a paratfinic hydrocarbon containing at least two carbon atoms into the resulting stream containing sa d combustion gas and acetylene at a rate sufiicient to crack said parafiinic hydrocarbon to ethylene and further reduce the temperature of the resulting stream of gases to between about 700 and 1100 C., and chilling the reacted mixture.

13. A process as defined in claim 12 wherein a pressure of about 2 to about 21 atmospheres (absolute) is maintained in the combustion zone, a pressure of about 0.9 to about 2 atmospheres (absolute) is maintained in the first pyrolysis zone, and a pressure of about 0.1 to 0.9 atmosphere (absolute) is maintained in the second pyrolysis zone.

14. A process for pyrolyzing hydrocarbons to produce unsaturated C, hydrocarbons, which comprises introducing methane into a combusiton gas which is free irom an excess of molecular oxygen and which has a temperature in the range from about 2600 C. to about 2400' C., adjusting the temperature of the hot gaseous mixture after the reaction to a range from about 1600 C. to about 1200 C. by regulating the amount of said methane, adding into the said hot gaseous mixture thus obtained at least one paraflinic hydrocarbon, containing at least two carbon atoms, in an atomized form, and adjusting the temperature of the hot gaseous mixture after the pyrolysis of the said paraffinic hydrocarbon to a range from about 1100 C. to about 700 C. by regulating the amount of said parafiinic hydrocarbon and chilling the reacted mixture.

References Cited in the tile of this patent UNITED STATES PATENTS 2,197,257 Burk July 14, 1936 2,371,147 Burk Mar. 13, 1945 2,706,210 Harris Apr. 12, 1955 2,767,233 Mullen et a1 Oct. 16, 1956 2,789,149 Bogart et al. Apr. 16, 1957 2,790,838 Schrader Apr. 30, 1957 2,822,411 Braconier et al. Feb. 4, 1958 2,823,243 Robinson Feb. 11, 1958 

1. IN THE PROCESS FOR THE MANUFACTURE OF UNSATURATED C2 HYDROCARBONS BY INTRODUCING METHANE INTO A COMBUSTION GAS WHICH IS FREE FROM AN EXCESS OF MOLECULAR OXYGEN, THE IMPROVEMENT WHICH CONSISTS IN ADDING TO THE HOT GASEOUS MIXTURE THUS OBTAINED AND HAVING A TEMPERATURE IN THE RANGE FROM ABOUT 1600*C. TO ABOUT 1200*C., AT LEAST ONE PARAFFINIC HYDROCARBONS CONTAINING AT LEAST TWO CARBON ATOMS, IN AN ATOMIZED FORM, AND ADJUSTING THE TEMPERATURE OF THE HOT GASEOUS MIXTURE AFTER THE PYROLYSIS OF THE SAID PARAFFINIC HYDROCARBON TO A RANGE FROM ABOUT 1100*C. TO ABOUT 700*C. BY REGULATING THE AMOUNT OF SAID PARAFFINIC HYDROCARBON, AND CHILLING THE REACTED MIXTURE. 